An electrical power system, or line, is a network of electrical components that is configured to deliver electromagnetic energy from at least one source to at least one load. An electric device is commonly used in such systems to transmit electrical power.
An electric device typically comprises an inner signal conductor which serves to transmit the desired electrical power between a source and a load. The inner conductor is separated from an outer conductor by an insulating material, or dielectric material, with the outer conductor being typically grounded. In electrical power conditioning devices, internal components or circuits are often arranged between the inner conductor and the outer conductor to reduce unwanted electrical energy.
High frequency energy, or noise, (e.g. of the type causing electromagnetic interference) is often introduced into the transmission line of electrical power systems. As can be appreciated, the presence of electrical noise can cause system malfunction or interference with sensitive circuits, and, as such, is removed to the greatest extent possible.
A low-pass filter is one type of electrical power conditioning device that is commonly incorporated into electrical power systems to suppress high frequency energy. For ease of installation into electrical power systems, low-pass filters are commonly integrated into coaxial electric devices, with the filter circuit extending between the inner power through conductor and the grounded outer conductor.
In use, a low-pass filter contained within an electric device allows for power with a frequency lower than a designated cutoff level to be transmitted along the inner conductor and, in turn, delivered to the intended load. By contrast, electrical energy present along the inner conductor with a frequency above the defined cutoff is attenuated and thereby substantially eliminated from transmission to the intended load.
Low-pass filters have various constructs but typically include at least one capacitor for removing unwanted high frequency energy. For instance, a shunt capacitor filter is a simple, first-order, low-pass filter that includes a single shunt capacitor for attenuating undesirable alternating current (AC) signals. Higher-order filters with multiple attenuating components, such as a Pi filter, are also commonly utilized in noise suppression applications, but are often difficult to construct in a compact fashion, particularly within a limited-size coaxial device package.
Accordingly, in order to maintain a compact construction, low-pass filters are often designed using the smallest available component parts. Because ceramic capacitors are generally considered the most compact type of capacitor, ceramic capacitors are particularly well suited for use in low-pass filters. Furthermore, in addition to its compact construction, ceramic capacitors have a relatively high temperature range, particularly as compared to plastic film capacitors.
Although beneficial for at least the reasons set forth above, ceramic capacitors are often disfavored for use in low-pass filters due to their inherent fragility. In fact, ceramic capacitors routinely exhibit failure modes over time, such as short circuiting due to cracking or other structural defects. As can be appreciated, the shorting of a ceramic capacitor in a low-pass filter can result in arcing and overheating within the electrical power line, particularly when used to transmit direct current (DC) voltages.
Furthermore, it should be noted that, due to package size restrictions and other related factors, conventional electrical power conditioning devices with noise suppression capabilities are not typically designed to additionally treat transient voltages, particularly if the energy content is below of the filtering band frequency. For example, if a transient voltage has a pulse width longer than the reciprocal of the cutoff frequency of the filter, the transient voltage is substantially unaffected by the filter and, as such, is delivered through the filter. For obvious reasons, random electrical impulses or energy spikes, particularly if the transient energy is of a voltage substantially higher than the operating power voltage level of the power system, can be highly problematic to any sensitive electrical components located along the electrical power line.
Because of these risks, electrical power systems typically rely upon separate devices for filtering noise and suppressing transient voltages. Specifically, low-pass filters are commonly integrated into electrical power systems to remove high frequency electromagnetic energy transmitted along the transmission line. Further, transient voltage suppression devices, or suppressors, are commonly integrated into electrical power systems, at a separate location from the low-pass filters, to discharge any high voltage electromagnetic energy transmitted along the transmission line. Typically, voltage suppressors include one or more voltage suppression components, such as gas discharge tubes and/or diodes, which are conductively coupled to the transmission line, preferably at a location close to a potential impulse source, in order to immediately suppress any transient pulses of electromagnetic energy.